This invention relates to a process for the dry desulfurization of a combustion gas, and, more particularly, to a process for dry desulfurization of combustion gas, in which the combustion gas produced in a combustion space and contaminated with fly ash as well as gaseous pollutants is dedusted, in which the dedusted combustion gas is cooled with water to a temperature of 50 to 90.degree. C., is mixed with an absorbent consisting of CaO and/or Ca(OH).sub.2 and is supplied to a circulating fluidized bed comprising a fluidized-bed reactor, a separator and a return line, wherein the solid particles obtained in the separator are supplied in part to the fluidized-bed reactor and in part to that area of the combustion space which has a temperature of 850 to 1050.degree. C. The process is used for the desulfurization of exhaust gases, which are produced during the combustion of solid and liquid fuels, in particular coal and oil, and during the incineration of refuse and sewage sludge.
From the German Patent Document DE-PS 41 04 180 a process for the dry desulfurization of exhaust gases from a boiler system by adding calcareous sorbents is known, wherein coarsely ground lime (CaCO.sub.3) with an average grain size of 200 .mu.m is introduced into a section of the boiler system where the exhaust gases have a temperature of 800 to 900.degree. C., wherein upon cooling the exhaust gases are dedusted in a first electrostatic dust separator, whereupon the coarse-grained portion is ground to an average grain size of 5 to 10 .mu.m and the medium- and fine-grained portions are discharged from the system, wherein the portion ground to 5 to 10 .mu.m together with water and the exhaust gases is supplied to a circulating fluidized bed consisting of fluidized-bed reactor, separator and return line, and wherein the exhaust gases are finally dedusted in a second electrostatic dust separator and are discharged to the surroundings, and the CaSO.sub.3 - and CaSO.sub.4 -containing residues are returned in part to the fluidized-bed reactor and in part to the boiler system. In this known process, dedusting is effected in the first electrostatic dust separator disposed behind the boiler at a temperature of 90 to 160.degree. C., and the temperature of the circulating fluidized bed is adjusted to 50 to 90.degree. C. through a corresponding measured addition of water.
It is also known that in the dry desulfurization processes the conversion of the absorbents with SO.sub.2 is only completed when there is a stoichiometric excess of the absorbent. A comparatively small excess of absorbent is achieved when CaO or Ca(OH).sub.2 are used as absorbents for the dry desulfurization, and when the absorbents are fine-grained and thus reactive. However, in particular in a circulating fluidized bed part of the CaO or Ca(OH).sub.2 gets lost due to the formation of calcium carbonate. This side reaction has a disadvantageous effect on the stoichiometry of the desulfurization reaction, so that for the dry desulfurization the absorbent CaO and/or Ca(OH).sub.2 must still be added in a remarkable surplus; the ratio of SO.sub.2 :Ca (with reference to separated SO.sub.2) virtually lies above 1:1.3. Moreover, in the dry desulfurization processes failures occur, because due to a reaction of the HCl contained in the exhaust gas with the absorbent hygroscopic CaCl.sub.2 is formed, which is responsible for the formation of disadvantageous cakings and agglutinations in the exhaust gas cleaning plant.